IT. Expert System.

Java Standard Edition (SE)

JScrollPane


javax.swing

Class JScrollPane

  • All Implemented Interfaces:
    ImageObserver, MenuContainer, Serializable, Accessible, ScrollPaneConstants


    public class JScrollPane
    extends JComponent
    implements ScrollPaneConstants, Accessible
    Provides a scrollable view of a lightweight component. A JScrollPane manages a viewport, optional vertical and horizontal scroll bars, and optional row and column heading viewports. You can find task-oriented documentation of JScrollPane in How to Use Scroll Panes, a section in The Java Tutorial. Note that JScrollPane does not support heavyweight components.

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    The JViewport provides a window, or "viewport" onto a data source -- for example, a text file. That data source is the "scrollable client" (aka data model) displayed by the JViewport view. A JScrollPane basically consists of JScrollBars, a JViewport, and the wiring between them, as shown in the diagram at right.

    In addition to the scroll bars and viewport, a JScrollPane can have a column header and a row header. Each of these is a JViewport object that you specify with setRowHeaderView, and setColumnHeaderView. The column header viewport automatically scrolls left and right, tracking the left-right scrolling of the main viewport. (It never scrolls vertically, however.) The row header acts in a similar fashion.

    Where two scroll bars meet, the row header meets the column header, or a scroll bar meets one of the headers, both components stop short of the corner, leaving a rectangular space which is, by default, empty. These spaces can potentially exist in any number of the four corners. In the previous diagram, the top right space is present and identified by the label "corner component".

    Any number of these empty spaces can be replaced by using the setCorner method to add a component to a particular corner. (Note: The same component cannot be added to multiple corners.) This is useful if there's some extra decoration or function you'd like to add to the scroll pane. The size of each corner component is entirely determined by the size of the headers and/or scroll bars that surround it.

    A corner component will only be visible if there is an empty space in that corner for it to exist in. For example, consider a component set into the top right corner of a scroll pane with a column header. If the scroll pane's vertical scrollbar is not present, perhaps because the view component hasn't grown large enough to require it, then the corner component will not be shown (since there is no empty space in that corner created by the meeting of the header and vertical scroll bar). Forcing the scroll bar to always be shown, using setVerticalScrollBarPolicy(VERTICAL_SCROLLBAR_ALWAYS), will ensure that the space for the corner component always exists.

    To add a border around the main viewport, you can use setViewportBorder. (Of course, you can also add a border around the whole scroll pane using setBorder.)

    A common operation to want to do is to set the background color that will be used if the main viewport view is smaller than the viewport, or is not opaque. This can be accomplished by setting the background color of the viewport, via scrollPane.getViewport().setBackground(). The reason for setting the color of the viewport and not the scrollpane is that by default JViewport is opaque which, among other things, means it will completely fill in its background using its background color. Therefore when JScrollPane draws its background the viewport will usually draw over it.

    By default JScrollPane uses ScrollPaneLayout to handle the layout of its child Components. ScrollPaneLayout determines the size to make the viewport view in one of two ways:

    1. If the view implements Scrollable a combination of getPreferredScrollableViewportSize, getScrollableTracksViewportWidth and getScrollableTracksViewportHeightis used, otherwise
    2. getPreferredSize is used.

    Warning: Swing is not thread safe. For more information see Swing's Threading Policy.

    Warning: Serialized objects of this class will not be compatible with future Swing releases. The current serialization support is appropriate for short term storage or RMI between applications running the same version of Swing. As of 1.4, support for long term storage of all JavaBeans™ has been added to the java.beans package. Please see XMLEncoder.

    See Also:
    JScrollBar, JViewport, ScrollPaneLayout, Scrollable, Component.getPreferredSize(), setViewportView(java.awt.Component), setRowHeaderView(java.awt.Component), setColumnHeaderView(java.awt.Component), setCorner(java.lang.String, java.awt.Component), setViewportBorder(javax.swing.border.Border)
    • Constructor Detail

      • JScrollPane

        public JScrollPane(Component view,
                           int vsbPolicy,
                           int hsbPolicy)
        Creates a JScrollPane that displays the view component in a viewport whose view position can be controlled with a pair of scrollbars. The scrollbar policies specify when the scrollbars are displayed, For example, if vsbPolicy is VERTICAL_SCROLLBAR_AS_NEEDED then the vertical scrollbar only appears if the view doesn't fit vertically. The available policy settings are listed at setVerticalScrollBarPolicy(int) and setHorizontalScrollBarPolicy(int).
        Parameters:
        view - the component to display in the scrollpanes viewport
        vsbPolicy - an integer that specifies the vertical scrollbar policy
        hsbPolicy - an integer that specifies the horizontal scrollbar policy
        See Also:
        setViewportView(java.awt.Component)
      • JScrollPane

        public JScrollPane(Component view)
        Creates a JScrollPane that displays the contents of the specified component, where both horizontal and vertical scrollbars appear whenever the component's contents are larger than the view.
        Parameters:
        view - the component to display in the scrollpane's viewport
        See Also:
        setViewportView(java.awt.Component)
      • JScrollPane

        public JScrollPane()
        Creates an empty (no viewport view) JScrollPane where both horizontal and vertical scrollbars appear when needed.
    • Method Detail

      • setUI

        public void setUI(ScrollPaneUI ui)
        Sets the ScrollPaneUI object that provides the look and feel (L&F) for this component.
        Parameters:
        ui - the ScrollPaneUI L&F object
        See Also:
        getUI()
      • getVerticalScrollBarPolicy

        public int getVerticalScrollBarPolicy()
        Returns the vertical scroll bar policy value.
        Returns:
        the verticalScrollBarPolicy property
        See Also:
        setVerticalScrollBarPolicy(int)
      • setVerticalScrollBarPolicy

        public void setVerticalScrollBarPolicy(int policy)
        Determines when the vertical scrollbar appears in the scrollpane. Legal values are:
        • ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED
        • ScrollPaneConstants.VERTICAL_SCROLLBAR_NEVER
        • ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS
        Parameters:
        policy - one of the three values listed above
        Throws:
        IllegalArgumentException - if policy is not one of the legal values shown above
        See Also:
        getVerticalScrollBarPolicy()
      • getHorizontalScrollBarPolicy

        public int getHorizontalScrollBarPolicy()
        Returns the horizontal scroll bar policy value.
        Returns:
        the horizontalScrollBarPolicy property
        See Also:
        setHorizontalScrollBarPolicy(int)
      • setHorizontalScrollBarPolicy

        public void setHorizontalScrollBarPolicy(int policy)
        Determines when the horizontal scrollbar appears in the scrollpane. The options are:
        • ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED
        • ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER
        • ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS
        Parameters:
        policy - one of the three values listed above
        Throws:
        IllegalArgumentException - if policy is not one of the legal values shown above
        See Also:
        getHorizontalScrollBarPolicy()
      • setViewportBorder

        public void setViewportBorder(Border viewportBorder)
        Adds a border around the viewport. Note that the border isn't set on the viewport directly, JViewport doesn't support the JComponent border property. Similarly setting the JScrollPanes viewport doesn't affect the viewportBorder property.

        The default value of this property is computed by the look and feel implementation.

        Parameters:
        viewportBorder - the border to be added
        See Also:
        getViewportBorder(), setViewport(javax.swing.JViewport)
      • getViewportBorderBounds

        public Rectangle getViewportBorderBounds()
        Returns the bounds of the viewport's border.
        Returns:
        a Rectangle object specifying the viewport border
      • createHorizontalScrollBar

        public JScrollBar createHorizontalScrollBar()
        Returns a JScrollPane.ScrollBar by default. Subclasses may override this method to force ScrollPaneUI implementations to use a JScrollBar subclass. Used by ScrollPaneUI implementations to create the horizontal scrollbar.
        Returns:
        a JScrollBar with a horizontal orientation
        See Also:
        JScrollBar
      • setHorizontalScrollBar

        public void setHorizontalScrollBar(JScrollBar horizontalScrollBar)
        Adds the scrollbar that controls the viewport's horizontal view position to the scrollpane. This is usually unnecessary, as JScrollPane creates horizontal and vertical scrollbars by default.
        Parameters:
        horizontalScrollBar - the horizontal scrollbar to be added
        See Also:
        createHorizontalScrollBar(), getHorizontalScrollBar()
      • createVerticalScrollBar

        public JScrollBar createVerticalScrollBar()
        Returns a JScrollPane.ScrollBar by default. Subclasses may override this method to force ScrollPaneUI implementations to use a JScrollBar subclass. Used by ScrollPaneUI implementations to create the vertical scrollbar.
        Returns:
        a JScrollBar with a vertical orientation
        See Also:
        JScrollBar
      • setVerticalScrollBar

        public void setVerticalScrollBar(JScrollBar verticalScrollBar)
        Adds the scrollbar that controls the viewports vertical view position to the scrollpane. This is usually unnecessary, as JScrollPane creates vertical and horizontal scrollbars by default.
        Parameters:
        verticalScrollBar - the new vertical scrollbar to be added
        See Also:
        createVerticalScrollBar(), getVerticalScrollBar()
      • createViewport

        protected JViewport createViewport()
        Returns a new JViewport by default. Used to create the viewport (as needed) in setViewportView, setRowHeaderView, and setColumnHeaderView. Subclasses may override this method to return a subclass of JViewport.
        Returns:
        a new JViewport
      • setViewport

        public void setViewport(JViewport viewport)
        Removes the old viewport (if there is one); forces the viewPosition of the new viewport to be in the +x,+y quadrant; syncs up the row and column headers (if there are any) with the new viewport; and finally syncs the scrollbars and headers with the new viewport.

        Most applications will find it more convenient to use setViewportView to add a viewport and a view to the scrollpane.

        Parameters:
        viewport - the new viewport to be used; if viewport is null, the old viewport is still removed and the new viewport is set to null
        See Also:
        createViewport(), getViewport(), setViewportView(java.awt.Component)
      • setViewportView

        public void setViewportView(Component view)
        Creates a viewport if necessary and then sets its view. Applications that don't provide the view directly to the JScrollPane constructor should use this method to specify the scrollable child that's going to be displayed in the scrollpane. For example:
         JScrollPane scrollpane = new JScrollPane();
         scrollpane.setViewportView(myBigComponentToScroll);
         
        Applications should not add children directly to the scrollpane.
        Parameters:
        view - the component to add to the viewport
        See Also:
        setViewport(javax.swing.JViewport), JViewport.setView(java.awt.Component)
      • setRowHeader

        public void setRowHeader(JViewport rowHeader)
        Removes the old rowHeader, if it exists; if the new rowHeader isn't null, syncs the y coordinate of its viewPosition with the viewport (if there is one) and then adds it to the scroll pane.

        Most applications will find it more convenient to use setRowHeaderView to add a row header component and its viewport to the scroll pane.

        Parameters:
        rowHeader - the new row header to be used; if null the old row header is still removed and the new rowHeader is set to null
        See Also:
        getRowHeader(), setRowHeaderView(java.awt.Component)
      • setRowHeaderView

        public void setRowHeaderView(Component view)
        Creates a row-header viewport if necessary, sets its view and then adds the row-header viewport to the scrollpane. For example:
         JScrollPane scrollpane = new JScrollPane();
         scrollpane.setViewportView(myBigComponentToScroll);
         scrollpane.setRowHeaderView(myBigComponentsRowHeader);
         
        Parameters:
        view - the component to display as the row header
        See Also:
        setRowHeader(javax.swing.JViewport), JViewport.setView(java.awt.Component)
      • setColumnHeader

        public void setColumnHeader(JViewport columnHeader)
        Removes the old columnHeader, if it exists; if the new columnHeader isn't null, syncs the x coordinate of its viewPosition with the viewport (if there is one) and then adds it to the scroll pane.

        Most applications will find it more convenient to use setColumnHeaderView to add a column header component and its viewport to the scroll pane.

        See Also:
        getColumnHeader(), setColumnHeaderView(java.awt.Component)
      • setColumnHeaderView

        public void setColumnHeaderView(Component view)
        Creates a column-header viewport if necessary, sets its view, and then adds the column-header viewport to the scrollpane. For example:
         JScrollPane scrollpane = new JScrollPane();
         scrollpane.setViewportView(myBigComponentToScroll);
         scrollpane.setColumnHeaderView(myBigComponentsColumnHeader);
         
        Parameters:
        view - the component to display as the column header
        See Also:
        setColumnHeader(javax.swing.JViewport), JViewport.setView(java.awt.Component)
      • getCorner

        public Component getCorner(String key)
        Returns the component at the specified corner. The key value specifying the corner is one of:
        • ScrollPaneConstants.LOWER_LEFT_CORNER
        • ScrollPaneConstants.LOWER_RIGHT_CORNER
        • ScrollPaneConstants.UPPER_LEFT_CORNER
        • ScrollPaneConstants.UPPER_RIGHT_CORNER
        • ScrollPaneConstants.LOWER_LEADING_CORNER
        • ScrollPaneConstants.LOWER_TRAILING_CORNER
        • ScrollPaneConstants.UPPER_LEADING_CORNER
        • ScrollPaneConstants.UPPER_TRAILING_CORNER
        Parameters:
        key - one of the values as shown above
        Returns:
        the corner component (which may be null) identified by the given key, or null if the key is invalid
        See Also:
        setCorner(java.lang.String, java.awt.Component)
      • setCorner

        public void setCorner(String key,
                              Component corner)
        Adds a child that will appear in one of the scroll panes corners, if there's room. For example with both scrollbars showing (on the right and bottom edges of the scrollpane) the lower left corner component will be shown in the space between ends of the two scrollbars. Legal values for the key are:
        • ScrollPaneConstants.LOWER_LEFT_CORNER
        • ScrollPaneConstants.LOWER_RIGHT_CORNER
        • ScrollPaneConstants.UPPER_LEFT_CORNER
        • ScrollPaneConstants.UPPER_RIGHT_CORNER
        • ScrollPaneConstants.LOWER_LEADING_CORNER
        • ScrollPaneConstants.LOWER_TRAILING_CORNER
        • ScrollPaneConstants.UPPER_LEADING_CORNER
        • ScrollPaneConstants.UPPER_TRAILING_CORNER

        Although "corner" doesn't match any beans property signature, PropertyChange events are generated with the property name set to the corner key.

        Parameters:
        key - identifies which corner the component will appear in
        corner - one of the following components:
        • lowerLeft
        • lowerRight
        • upperLeft
        • upperRight
        Throws:
        IllegalArgumentException - if corner key is invalid
      • setComponentOrientation

        public void setComponentOrientation(ComponentOrientation co)
        Sets the orientation for the vertical and horizontal scrollbars as determined by the ComponentOrientation argument.
        Overrides:
        setComponentOrientation in class Component
        Parameters:
        co - one of the following values:
        • java.awt.ComponentOrientation.LEFT_TO_RIGHT
        • java.awt.ComponentOrientation.RIGHT_TO_LEFT
        • java.awt.ComponentOrientation.UNKNOWN
        See Also:
        ComponentOrientation
      • isWheelScrollingEnabled

        public boolean isWheelScrollingEnabled()
        Indicates whether or not scrolling will take place in response to the mouse wheel. Wheel scrolling is enabled by default.
        Since:
        1.4
        See Also:
        setWheelScrollingEnabled(boolean)
      • setWheelScrollingEnabled

        public void setWheelScrollingEnabled(boolean handleWheel)
        Enables/disables scrolling in response to movement of the mouse wheel. Wheel scrolling is enabled by default.
        Parameters:
        handleWheel - true if scrolling should be done automatically for a MouseWheelEvent, false otherwise.
        Since:
        1.4
        See Also:
        isWheelScrollingEnabled(), MouseWheelEvent, MouseWheelListener
      • paramString

        protected String paramString()
        Returns a string representation of this JScrollPane. This method is intended to be used only for debugging purposes, and the content and format of the returned string may vary between implementations. The returned string may be empty but may not be null.
        Overrides:
        paramString in class JComponent
        Returns:
        a string representation of this JScrollPane.
      • getAccessibleContext

        public AccessibleContext getAccessibleContext()
        Gets the AccessibleContext associated with this JScrollPane. For scroll panes, the AccessibleContext takes the form of an AccessibleJScrollPane. A new AccessibleJScrollPane instance is created if necessary.
        Specified by:
        getAccessibleContext in interface Accessible
        Overrides:
        getAccessibleContext in class Component
        Returns:
        an AccessibleJScrollPane that serves as the AccessibleContext of this JScrollPane


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